1. Field of Invention
The present invention relates to a method for obtaining electric power information and, in particular, to a method for obtaining electric power information of a power supply.
2. Related Art
Power supplies have been widely applied to various electronic apparatuses, such as PC, notebook computers, or servers. The precision of the inputted current for the power supply of any electronic apparatus has become more and more critical. For example, the allowable range of the input current for the old generation electronic apparatus, which is equal to or larger than 3 A, is about 5%; however, the allowable range of the input current for the present electronic apparatus is about 3% only. This difference indicates that to precisely obtain the input current of the power supply is very important.
The existing method for obtaining the input current of the power supply is to provide a power monitoring chip between the power supply and the input terminal. However, this method may easily cause the damage of the power monitoring chip, which results in the malfunction of the electronic apparatus. Besides, this method also needs the additional optical coupler and isolated auxiliary power source, which increase the manufacturing cost. Another method is to estimate the input current of the power supply by the digital signal processor or single chip of the primary/secondary power factor correction (PFC) circuit. Unfortunately, this method can only directly estimate the real power instead of the input current of the power supply. In this method, an additional current transformer (CT) between the power supply and the input terminal is needed to obtain the input current of the power supply, which also increases the manufacturing cost.
Besides, the power supply must contain an X-capacitor for the safety consideration. Since the X-capacitor is connected with the AC power source in parallel, the accuracy of the capacitance of the X-capacitor can directly affect the precision of the input current of the power supply.
Therefore, it is an important subject to provide a method for obtaining electric power information can precisely estimate the input current of the power supply or the capacitance of the X-capacitor without the additional cost for the optical coupler, isolated auxiliary power source or current rectifier.